1. Field of the Invention
The present invention relates to semiconductor manufacturing equipment. More particularly, the present invention relates to an apparatus and method of dispensing photosensitive solution, such as photoresist, onto a semiconductor wafer.
2. Description of the Related Art
The recent rapid development of information processors, such as computers, has brought about remarkable advances in semiconductor devices, e.g., in semiconductor memory devices. These devices must be highly integrated if they are to be competitive in the marketplace, i.e., if they are to be of high quality yet low in cost to manufacture. One way to achieve a high degree of integration in a semiconductor device is to scale down components of the device. For example, the thickness of a gate oxide or the channel length of a transistor of the device can be reduced. To meet the current demand for high-performance devices, semiconductor manufacturing processes and manufacturing equipment must, therefore, be continuously improved. That is, the performance of semiconductor device manufacturing equipment is becoming increasingly more important.
In general, the manufacturing of semiconductor devices entails forming numerous patterns on a wafer. Accordingly, semiconductor manufacturing equipment includes a transfer robot for transferring wafers throughout the equipment, a coater for coating the wafers with photosensitive solution, a bake unit for baking the photosensitive solution on the wafers such that a layer of photosensitive material is formed on the wafers, an aligner for orienting the wafers to a predetermined position, an exposure unit for exposing the photosensitive material to light directed through a photomask or reticle bearing a pattern, a developing unit for developing the exposed photosensitive layer such that the photosensitive layer is patterned, and an etching unit for etching a target layer on the wafer using the photosensitive layer pattern as an etch mask. As a result, the target layer is patterned in correspondence with a pattern borne by the photomask or reticle.
A coater of the semiconductor manufacturing equipment includes photosensitive solution dispensing apparatus having a configuration as generally shown in FIG. 1. More specifically, the photosensitive solution dispensing apparatus includes supply vessels 10 and 11 for storing photosensitive solution such as photoresist, first and second tanks 20 and 21 for buffering the photosensitive solution supplied from the supply vessels 10 and 11 so as to uniformly dispense photosensitive solution, a pump 42 for pumping photosensitive solution from the first and second tanks 20 and 21, a filter unit 47 including filters 48 and 49 for removing air bubbles from the photosensitive solution, and a nozzle 52 for spraying the filtered photosensitive solution onto a surface of a wafer 60 while the wafer 60 is rotated. Also, a drain line extends from the filter unit 47 and a drain valve 50 allows for solution to be drained from the filter unit 47.
The photosensitive solution dispensing apparatus also includes several other lines/pipes 15, 16, 23, 24, 30, 31, 37, 38, 40, 44 and 45 through which the photosensitive solution can flow, and valves 27, 28, 33, 34 and 50 that control the flow of the photosensitive solution through the apparatus. Lines 15 and 16 extend, respectively, between supply vessels 10 and 11 and first and second tanks 20 and 21. Lines 23 and 24 are drain lines used to discharge photosensitive solution and air from each the first and second tanks 20 and 21, respectively. The valves 27 and 28 are provided in the lines 23 and 24 to control the draining of the first and second tanks 20 and 21. Solution stored in each of first and second tanks 20 and 21 is supplied to an inflow line 40 of the pump 42 through lines 30, 31, 37 and 38. Valves 33 and 34 are disposed in the lines 30 and 31, respectively, and are positionable to selectively allow or prevent the flow of solution from the tanks 20 and 21 to the inflow line 40. Line 44 extends between the pump 42 and filter unit 47, and photosensitive solution filtered by the filter unit 47 flows to the nozzle 52 through outlet line 45.
In addition, the photosensitive solution dispensing apparatus includes sensors 18 and 19 for sensing air bubbles within the first and second tanks 20 and 21, respectively. Each of the sensors 18, 19 includes a light emitting part (light emitter) and a light receiving part (light receptor).
Photosensitive solution, such as photoresist, is supplied from the supply vessels 10 and 11 onto the wafer 60 through nozzle 52, as follows.
In the case in which photosensitive solution stored in supply vessel 10 is to be dispensed onto the wafer 60, valve 34 is closed, and valve 33 is opened. The opening/closing of the valves 33 and 34 is automatically controlled by a controller of the photosensitive solution dispensing apparatus. Next, the pump 42 is driven to draw photosensitive solution temporarily stored in the first tank 20 through lines 30, 37 and 40. From there, the photosensitive solution is pumped to the filter unit 47 through line 44. The photosensitive solution filtered in the filter unit 47 is outputted to line 45 and hence, is dispensed by the nozzle 52 onto wafer 60.
Accordingly, the amount of photosensitive solution stored in the supply vessel 10 is gradually reduced. Eventually, air bubbles start to fill the first tank 20. The sensor 18 generates a signal once a predetermined volume of the tank 20 becomes occupied by the air bubbles. At this time the supply vessel 10 must be changed. Accordingly, the controller generates a control signal that opens valve 34 and closes valve 33. While the valve 34 is opening, nitrogen gas is introduced into the supply vessel 11 through line 14. The pressure of the nitrogen gas discharges bubbles existing in the line 16 and second tank 21 through line 24 and drain valve 28. However, micro bubbles may flow into line 44 through the pump 42 because the pressure of the nitrogen gas may not be sufficient to discharge the micro bubbles through the line 24 and drain valve 28. Thus, the photosensitive solution discharged through nozzle 52 may contain bubbles. In this case, the photosensitive layer formed on the wafer 60 may be defective.
More specifically, with reference to FIG. 2, although some of the micro bubbles are discharged through drain valve 28, most of the micro bubbles MA remain in the tank 21. These micro bubbles MA are entrained in the photosensitive solution and thereby migrate to the pump 42 through line 30, valve 33 and line 37. Eventually, the micro bubbles diffuse within the photosensitive solution in line 44 (FIG. 1), and then gradually accumulate within the filter unit 47. Hence, bubbles are mixed with the photosensitive solution discharged through the nozzle 52, thereby reducing the volume of solution that is being dispensed. As a result, the quality of the photosensitive layer is adversely affected. Such a defect in the photosensitive layer may give rise to errors in subsequent steps of the photolithographic process.